Before fishing: SET THE DRAG, check the line for nicks and kinks, a quick once over to make sure everything is working properly.
During fishing: Wipe off any dirt, especially in the line guide.
After fishing; Loosen the drag, wipe down and put a drop of oil (never grease) on the worm gear.
At least once a year: Tear down, clean thoroughly, grease the drive train, oil the bearings (more often on reels that see heavy use), replace any worn parts and put them away (in Crown Royal bags) until net season.
Do this religiously and your reels should serve you faithfully for many years.
Tom